The present invention relates to a valve gating apparatus for use with injection molds. More specifically, the present invention relates to an apparatus for laterally gating the flow of molten materials from an injection-molding nozzle into a mold cavity.
In the field of injection molding, it is known that some means must be provided to inhibit the flow of molten material into the cavity of a mold so that the mold may be cooled and opened to remove the molded part. One way of achieving this inhibition is by valve gating, wherein a mechanical means is employed to inhibit the flow of material being injected into the mold cavity.
Lateral valve gating is one type of valve gating that has been developed. In lateral valve gating systems, a valve member is moved across the melt flow before or after the gate to block or allow flow through the gate. Some lateral valve gating systems typically use a stamped, or machined (one-piece) rail as the valve member. However, one-piece rails suffer from certain problems and disadvantages. For example, because the top gate on the rail carries the full cutting force of the entire rail, a one-piece rail suffers from fatigue failure through the gate area. Fatigue failure also exists through the rail clamping area due to the thin sections of a one-piece rail design. Further, high stress concentrations exist at the gate corner as a result of rail loading and the one-piece rail design.
Another problem with the one-piece rail design gating systems is the difficulty in achieving rail gate alignment between subsequent pairs of gate pad posts and rail gates. The one-piece rail design induces excessive side loads on the rail gates which cause binding, excessive actuation forces to move the rail, and premature rail failures.
See also U.S. patent application Ser. No. 09/036,132 now U.S. Pat. No. 6,146,123, Ser. No. 09/377,996, No. 09/372,174 now U.S. Pat. No. 6,149,417, and Ser. No. 09/030,593 now U.S. Pat. No. 6,056,536, the subject matter of which are incorporated herein by reference. The art cited in those is also incorporated herein by reference.
It is desired to have an apparatus for use in injection molding operations which reduces or eliminates the problems and disadvantages that exist with lateral gating systems that utilize one-piece rail design.
It is an object of the present invention to provide a novel valve gating apparatus for use in injection molding operations.
According to one aspect of the present invention, there is provided a valve gating apparatus for an injection mold nozzle assembly including a melt channel and a nozzle gate, said valve gating apparatus being positioned between the nozzle gate and a mold cavity, comprising:
at least one shutter movable between a first position wherein said shutter inhibits flow of melt material from said nozzle gate and a second position wherein said gate is in fluid communication with said mold cavity, and wherein said shutter is removably fastened to a rail member;
means to move said rail member substantially perpendicular to the direction of melt flow through said nozzle gate between first and second positions.
The present invention virtually eliminates the problems of fatigue failure that exists in one-piece rail designs. Unlike in the stamped rail design where the top gate on the rail carries the full cutting force of the entire rail, with the insert design of the present invention, a single insert carries the cutting load (force) for a single gate. Also, the xe2x80x9cfloatingxe2x80x9d aspect of the insert design eliminates side loading between subsequent gates on the rail, and therefore eliminates fatigue failures through the gate area of the rail. Furthermore, the rail clamp end design allows for greater clamping flexibility and reduces fatigue loading through the clamp area, thus eliminating fatigue failures in that area as well.
The present invention also virtually eliminates rail stretch between subsequent gates because the rigid xe2x80x9ccarrierxe2x80x9d portion carries the full shear load during operation and the cross-sectional area and geometry of the rigid xe2x80x9ccarrierxe2x80x9d portion of the rail are significantly different from the one-piece rail. Since rail stretch is eliminated, the need to design progressive gate spacing between subsequent gates is also eliminated and this results in the reduction of manufacturing costs. In addition, increased manufacturing tolerances on the gate pad post location and gate opening in the insert allow for a further reduction of manufacturing costs.
Other benefits of the present invention relate to the serviceability and service life of the component. Because of the design, individual inserts can be quickly replaced without the need for readjusting the position of the entire rail. With the one-piece design the entire rail must be replaced and manually readjusted even if a single gate location was damaged. The replaceable insert design significantly reduces replacement and maintenance costs. In addition, the service life of the present invention is much greater than that of the one-piece design, because the one-piece design was prone to failure after a finite number of cycles.
Furthermore, the insert design allows for the insert to be made of a different material than the rail itself. Earlier embodiments could not provide this feature since the rail itself was the element that opened and closed the channel.